Ideas, experiments and other camera adventures and tutorials

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Monthly Archives: September 2012

There are a multitude of programs to handle and process HDR. Today almost all standard photo editing software have some kind of support for it – with varying degrees of freedom and finesse.
Photoshop have had it for quite some time as well has other more or less high end photo editing software. The one I like the best, and that I use almost exclusively, is Photomatix Pro.
Photomatix is done by a small company called HDR soft and they have a very nice and reasonable licensing scheme. First of all, you can download it for free and try it out. This gives you some limitations as well as watermarks all over. Still, you will not by it without knowing its capabilities.

Secondly, once you have bought it – it is yours. You have a personal license key that you can use on all your computers. The only requirement is that you only use the software on one installation at the time. This, I believe, makes sense to a lot of people that have laptops and stationary computers that they use interchangeably. It also covers different architectures. So if you have a stationary PC and a MAC laptop you can have the same license on them!
I have used Photomatix for close to three years and so far all upgrades has been for free – also something to note when you compare to certain other larger companies..
I get nothing from pitching Photomatix! I just wish HDR soft to be successful and for you to find this nice, cheap tool.

I friend of mine introduced me to HDR (High Dynamic Range) photography. It’s interesting while at the same time being a new challenge in itself. The challenge is that you combine a number of pictures into one. This is typically done using the cameras multi-bracketing feature.
That means that the camera is instructed to make several exposures using various exposure compensations. A typical scenario would be to have the camera set to +-2 EV using three brackets.
That will result in 3 pictures being taken. One with normal exposure, one with +2 EV exposure (over exposed) and last one with -2 EV exposure (under exposed). When these pictures are combined a total image is composed which much higher dynamic range – that means high detail in both the dark and light areas.
During normal, single exposure photography, one has to choose which area to focus on or rather, to prioritize in terms of lightning. Depending on the camera this may have different names and different algorithms. In some modes an average is used and in other modes a single spot is chosen. In all cases though, the camera is not able to achieve the same dynamics that the human eye can handle. A common example is taking a picture indoor on a sunny day. The human eye has no problem in seeing both the interior of the room together with what is seen through a window from the outside. This can typically never be done with a normal camera with a single picture. You have to choose either to make the room look good (with the exterior being just a white spot) or the exterior to look good (with the interior of the room in more or less darkness).
Going back to the challenges of HDR. We have now taken the pictures and merged them together and should now have the same dynamic range (or better) than our eyes have. Unfortunately the computer displays as well as the printers we use also have a limited dynamic range. So in order to show the HDR picture we now have to compress the range into something that can be displayed or printed. If we just squeezed it back together without any hint of what we want to prioritize then we’re back where we started. Instead there are different approaches which lead to a more or less natural look. Depending on your taste you may find the result to be everywhere from ugly, surrealistic to really nice.
I tend to use HDR in a number of different areas – all quite different goals. I encourage you to try this for yourself and find your own favorite subjects.

It’s kind of nice when you have reached a point where your tools are more than capable of the task at hand – but it turns out that manual work is more efficient. I had this idea of glasses with liquid that where spraying out (kind of my previous glass drops, see previous post) but with a lateral movement. In the end I used a skateboard and taped the glasses to it. The idea was to get a collision that got the liquid moving but then changed direction.
After several tries it turned out that manual triggering was more accurate than all electronics I had built. Strange? Well, it’s easier to look at the result and just try again than trying to adjust the parameters of the trigger when the largest source of error is still you trying to get the same momentum of the skateboard.

When the drop re-bounces from the liquid it forms a column that shoots out towards in the opposite direction. With enough timing it is possible to have a second drop hit that column during its short life span to get other spectacular results.
Many parameters are now affecting the final result and some kind of programmable hardware is required to control the results. It is still possible to get nice results with “normal plumbing” things but, well, it may take a lot of time. And maybe quite frustrating.
In these pictures I used green food coloring in the water that was dropped.
The above picture shows the re-bounce of the the first drop and the arrival of the second drop. One rather amazing thing to note is that the initial drop is still quite intact. Notice the color difference between the first drop (the one behind) and the column? In this picture the alignment of the two drop were not perfect.
In this picture the alignment was better (with all windows closed!) and you can see how the two drops start to collide.
Mixing different liquids will make the collision stand out even more. In the following pictures I used milk as the liquid surface. I recommend whole milk as it has higher surface tension.
Similar setup but with colored water drop colliding with milk. Each time you prepare and start fine tune your setup it is important to decide what you want to achieve and with what materials. Since the behavior of for instance water and whole milk is so different all timing will have to be redone. The same is true if you, late in the work process, decide that you want smaller drops and add some rinse aid. After this the drop size will change and all timing. Still, it is great fun and I encourage you to try and experiment!
Once I had everything setup as I wanted and was experimenting with different drop sizes and intervals I realized that it was possible to sequence the initial stepping. If we consider the time from start to exposure of the frame as an equation of the form:

TimeToExposure = OpenTime0+ Delay0 + OpenTime1 + Delay1 where

OpenTime0is the amount of time the valve is open to release liquid for 1st drop (this determines the size of the drop).

Delay0 is the amount we wait until the valve is opened for the second drop

OpenTime1 is the time the valve is open for the second drop

Delay1 is the time we wait until the picture is taken

Then altering Delay1 while keeping the other parameters unchanged will yield pictures where things will progress as though they were taken very fast during one single event. Of course there will be variations and many parameters will come into play. Make sure there is as little movement of air as possible (these drops are very light and will be moved by even small air flows. Other aspects are the drip device you use and whether there is randomness in the flow and release. Anyhow, once I had this working I realized it was possible to make a “fake high speed camera movie” of the collision of two water drops. And here is the result:

One tell-tale here of the fact that this is not a high-speed movie is the fact that I use food coloring for the drop. Since the movie consists of close to 300 picture – that means 600 drops – the color of the milk slowly turns green…Yes, I could have changed the milk every frame but I’m lazy . Still, it’s kind of nice to have reproducible results that your can alter to become the composition of your choice!

Capturing fast events that are otherwise missed by the naked eye is fascinating. Things that we see everyday and believe to know how they happen are sometimes much more complex. With beautiful, otherwise invisible, in-between states.

One such example is the life of water drop as it hits a surface. As the drop hits the surface a corona is formed around the center. This can be done with both a hard surface as well as with a liquid surface to land on. As the event we want to capture is very quick it is important to either have very good lightning and fast shutter speed or use a flash to control the exposure time. See previous posts on High Speed Photography.

Depending on the speed of the drop, the surface tension of the fluid it lands in and several other parameters there may also be a re-bounce. By altering the mixture of the the liquid that is dropped and the liquid that it lands in it is possible to achieve very different re-bounces.

Food coloring can be used to give both the drop and/or the the liquid to land in different appearances. To control the surface tension I use dishwasher rinse aid. Corn starch can also be used to increase the surface tension (rinse aid reduces the surface tension). Another variable to use is different colored screen to get alternate colors.

Then with varying drop size and timing it becomes possible to shape the column formation to achieve different shapes and expressions.

There are other ways to achieve High Speed Photography but everything I’ve written here is based on using normal equipment and not ultra special hardware that can film at 500+ frames per second.

The idea is simple but requires the room/environment to be dark. It works like this:

The camera is set to manual exposure with the aperture chosen so that you get the depth of view desired. You can either experiment with this to get the result you want or use a tool like this to calculate it. ISO should be as low a possible while still getting the exposure you want to minimize noise. Focus should also be preset manually.
If the environment is dark enough then the time of the exposure will essentially be the burn time of the flash. Most flashes can be set to different power outputs. It is usually stated in parts of full power e.g. 1/4 means a quarter of full power. Experiment with different flash power, aperature and ISO to get the exposure you want. Remember that the farther you are from full power of the flash the shorter the burn time will be. The total time a normal flash is lit, or the energy discharged, is around 1/1000 of a second (1 ms). If you lower the flash output then this time is made shorter. That is how normal camera flashes work. This does not apply to studio flashes which lower the voltage to control the flash power.
A really good article on this can be found here here are some numbers from the article (they are for an old Canon Flash called 430 EZ):

At full (1/1) power the flash is lit for 1/1000, 1 ms or 1000 us.

At 1/4 power the flash is lit for 1/1064 or 940 us.

At 1/8 power the flash is lit for 1/2730 or 365 us.

At 1/16 power the flash is lit for 1/6450 or 155 us.

At 1/32 power the flash is lit for 1/11400 or 88 us.

…

This means that with a powerful flash and low power output it is possible to achieve exposure times much shorter than what the camera itself can accomplish with the shutter. If the environment is dark enough you can have the camera set to Bulb or 1 second and still capture really fast moving objects.